Mel Fisher, whose notorious optimism in the face of death, debt and doubting investors led him to the richest shipwreck in history, must wonder where the good times have gone.

Thirteen years after striking a treasure trove in the azure waters of the Florida Keys, a Spanish galleon that has already yielded $500 million, Mr. Fisher is fighting a state suspicion that he sold fake coins, a Federal court finding that he harmed the environment and an international movement to rein in private salvage, a business Mr. Fisher personified with his motto, ''Finders keepers.''

At a gathering of 200 investors that was interrupted by a police raid and seizure of suspected forged coins from his shop, the 75-year-old Mr. Fisher, bent and bald from chemotherapy, admitted, ''It hasn't been that good a year.''

That's for sure. He had to dip into his private stash of coins and emeralds to insure a return to his faithful. With the new accusations of fraud against him this spring, he is again being dogged by those who call him a modern-day pirate. And Mr. Fisher is not the only one in the industry under siege; in many ways the golden age of treasure hunting appears to be over.

Environmental, cultural and historical forces are merging to alter the practice of shipwreck salvage. Along America's traditionally laissez-faire coastline, new regulations are placing wrecks off limits or making them tough to retrieve. Of thousands of known wrecks, fewer than 20 are under salvage permit. Half are Mr. Fisher's.

Even offshore, in what had been unregulated ocean where salvagers go in search of the ultimate payoff, there is no peace. At the urging of archeologists and historians from many countries, the United Nations will begin debating June 29 in Paris a treaty to protect shipwrecks worldwide.

''I don't think private salvage will exist in five years,'' said Ben Benson of Sea Hunt, an explorer who in March spent $7,000 a day for legal fees to clear permits for two Spanish wrecks off Virginia. ''It's one of the last bastions of pure, free enterprise and risk taking, and it doesn't seem to fit into the regulatory society we seem to be in.''

Archeologists say underwater treasures deserve the same protection as artifacts on public lands.

''With new technology, salvage operators can find and destroy every shipwreck on the planet,'' said Larry Murphy, an archeologist with the National Park Service.

No one faces the pressure to change like Mr. Fisher, a former chicken farmer who, after finding a doubloon off Florida in the 1960's, began chasing X's on treasure maps. At the time, salvage was based on British Admiralty law, which considered the work of salvagers in the public interest.

American law was written here in the Florida Keys, where salvagers raced to wrecks on the reef, then filed claims in Federal court. Rights to salvage the Titanic were rewarded that way. In a Supreme Court case, Mr. Fisher extended the law to abandoned shipwrecks.

With the invention of huge sand blasters, sensitive magnetometers and side-scan sonar dragged over thousands of miles of ocean, Mr. Fisher turned a snorkeling hobby into what one archeologist called strip mining. It was boring work. Bombs, beer cans and even a sunken Volkswagen caused false alarms. Mr. Fisher spurred his workers with the motto ''Today's the Day,'' even after a son and daughter-in-law drowned. He was most inventive in raising $13 million for 18 years of hunting. Living on a houseboat that sank frequently, Mr. Fisher sold shares in several companies, sold coins as he found them, sold diving excursions to the wrecks. He wrote out one deal on a cocktail napkin that turned out to be worth millions when, in July 1985, he finally found the mother lode of the Atocha, a Spanish galleon that went down in 1622.

Archeology took a back seat as silver coins, gold chains and artifacts were hauled 50 feet from the ocean floor in milk crates. There were so many shoe-box-sized silver ingots that at Mr. Fisher's ramshackle headquarters here, his staff dismisses them as doorstops.

The Atocha created a handful of millionaires, including the Fisher family, said David Paul Horan, Mr. Fisher's lawyer at the time. It also made a folk hero of Mr. Fisher, especially in Key West, where boats and businesses were purchased with treasure and dozens hang Atocha coins around their necks.

But others have long accused him of salting the dive site and exaggerating the value of treasure.

Mr. Fisher has never lost a court case, Mr. Horan said, but he has settled several with treasure. One lawyer, who was paid with treasure he later called fake, forced a special prosecutor's investigation. A grand jury declined to bring charges.

Today, Mr. Fisher sells one-year limited partnerships for a 35 percent share in his continuing hunt, for amounts ranging from $6,250 to $400,000.

Jean Thornton, a public school counselor from Birmingham, Ala., who invested $6,250 after posing for a photo draped in Mr. Fisher's gold chains, sold her first year's emerald for $10,000 and reinvested. Now she has signed on for a third year. ''I'm kinda hooked is what I am,'' she said.

Kim Fisher, Mel's son, said the other half of Treasure Salvors' $1.7 million budget comes from selling artifacts and coins, most of which come with a certificate of authenticity signed by Mr. Fisher, a marketing device that elevates $7 in silver bullion to an $1,800 keepsake. Of 90,000 marketable Atocha coins, all but 3,000 have been sold.

This spring, an investor who paid $5,900 for a gold coin said to be from a 1733 Spanish fleet became suspicious and asked the authorities to investigate. Kirk Zuelch, state attorney for Monroe County, said that coin and 35 others seized at Mr. Fisher's shop and supplied by other customers since the raid are counterfeit, according to two experts his investigators consulted. They say the coins contain too much gold and lack distinctive details. Mr. Zuelch has not decided whether to file charges.

''Fisher has sold lots of authentic coins -- why would a man, at his stage in life, get caught up in something like this?'' rhetorically asked one state expert, Dr. Alan Craig, a retired professor of Latin American studies. ''He's learned that there is always someone who wants to buy into the romance of get rich quick.''

Mr. Fisher says he has never sold fake coins but concedes that he signed the certificate saying he found the coins, when, in fact, he bought them for less than $1,000 apiece from Walter J. Kruse, a longtime associate who in 1975 was convicted in Pennsylvania of selling fake coins. Mr. Fisher says he did not know about the conviction, but with his credibility damaged, he has hired metallurgy experts who he says support the coins' authenticity.

Mr. Fisher's ability to sell dreams and shrug off doubters may have no equal in the treasure world, but his success has come back to haunt him.

The Atocha discovery spawned a scramble for treasure, with 50 shipwreck claims filed in American waters in the next few years. It also galvanized archeologists, historians and environmentalists, who feared the loss of priceless artifacts and the destruction of eco-systems.

In 1987 Congress approved the Abandoned Shipwreck Act, which ended Admiralty law and gave states title to wrecks within three miles of the coastline. In the decade since, states have virtually stopped writing salvage permits and 541 underwater sites have been placed on the National Register of Historic Places, said Anne G. Giesecke, who wrote the act.

Mr. Fisher, who has six salvage permits that were grandfathered into the law, is appealing a $589,000 fine imposed by a Federal judge last year after another son blew 100 craters in sea grass inside the Florida Keys Marine Sanctuary. Billy Causey, the sanctuary's superintendent, said it was not his intention to stop treasure hunting. ''Our job is to protect the resource,'' he said. ''But you can't build a house in the Keys the way you did in the 50's.''

The proposal before Unesco's panel of experts at their coming meeting extends this idea to the edge of the continental shelf of every country, a 200-mile cultural heritage zone that would require salvagers to file research plans and apply to the ship's country of origin.

The specific language will be debated for quite a while, officials say, but with the writing on the wall, modern salvage operators have proposed a number of alternatives to ''finders keepers.''

One group of prominent salvagers formed a professional association ''to write standards, to better police our activities and establish a certain level of credibility for our operations,'' said Peter Hess, a lawyer coordinating the effort.

Salvagers want to preserve the right to sell artifacts to collectors. But the newest wrinkle is the private, for-profit collection. Barry Clifford of Provincetown, Mass., is salvaging the Whydah, a pirate ship whose crew included escaped slaves, and charging admission. ''I can't bring myself to divide and sell it,'' he said.

RMS Titanic Inc. is netting $1 million every three months from three traveling exhibits of 5,000 artifacts. ''The company has not recovered its $20 million investment, but we have an appreciating asset,'' said its president, George Tulloch.

In fact, few if any of Mr. Fisher's imitators have recouped their investments. One 1990 study of 20 shipwrecks found that just one -- Mr. Fisher's -- made money. In this century, only one other wreck the Atocha's size has been found, the Central America off South Carolina, with $1.2 billion in coins and bullion.

As known wrecks are picked over and hunts move offshore, the risks and costs for investors increase. With modern technology, many believe that another golden age of salvage will begin after deepwater regulations are decided. But the treasure may be history, not gold, said Paul Johnston, curator of maritime history for the Smithsonian Institution, who is excavating the royal yacht of the King of Hawaii, sunk in 1824. ''Where we have made progress is in recognizing that these are limited resources that need to be protected for the benefit of all, not just a few salvagers who want to line their pocket,'' he said. ''This is a diminishing marine resource, like whales, that need some kind of international care.''

Mr. Fisher, whose fight with cancer began about the time he discovered the Atocha, insists his business will survive him, as his children take over. In the meantime, he still runs the business of selling dreams.

''Look at this,'' he said to a group that stepped into his office not long ago, pointing out a pattern of sonar echoes, the modern equivalent of the X on a treasure map. ''If that's what I think it is, we've found the Margarita, 40 tons of gold and silver and over $2 billion in emeralds and lots of other stuff.''

''Really? No!'' said one visitor. Without missing a beat, Mr. Fisher slid over a blank contract seeking $50,000.